Relating to pyrotechnic ammunition

ABSTRACT

A cartridge comprising a casing ( 1 ) having a passage extending therethrough, said passage having a larger diameter rearward section ( 7 ) and a smaller diameter forward section ( 9 ). A core member is slidably received in the passage, and has a forwardly facing piston surface ( 21 ) and a portion ( 19 ) closing the forward length of passage in the unactivated condition of the cartridge. A cavity ( 23 ) within the core member receives propellant gas from a primer ( 25 ) and discharges the gas into the passage forwardly of the piston surface. The core is propelled rearwardly and releases propellant gas into the forward passage section.

WO 95/05573 relates to a gas cartridge which can be used as analternative to cartridges activated by pyrotechnic mechanisms. U.S. Pat.No. 4,686,905 relates to a pyrotechic cartridge for a frangibleprojectile.

European patent specification EP 473 758 relates to non-lethalpyrotechnic ammunition for training and war games. A cartridge disclosedin this earlier specification includes a casing slidable relative to aplug at the forward end of the cartridge. When the cartridge is fired,force provided by the propellant gas is employed to urge the casing backagainst the breech-block and recycle the weapon.

This known cartridge is charged with a small quantity of propellant inaddition to that contained in a primer. In order to achieve theobjective of the cartridge, the propellant gas is fed through relativelyconstricted passages and galleries. Filling and machining tolerancesmean that variations often occur in the weight of the additionalpropellant, and in flow rates through the passages and galleries, andlead to unreliable performance.

This problem is overcome by the cartridge herein proposed, which willnow be described with reference to the accompanying drawings, in which:

FIG. 1 is an axial section through a round of ammunition whichincorporates the proposed cartridge, showing the round in positionwithin the barrel of a gun, before firing,

FIG. 2 is a view similar to FIG. 1, showing the parts of the cartridgein the positions they occupy immediately after ignition of the primer,

FIG. 3 is a view similar to FIG. 1, showing the parts of the cartridgein the positions they occupy immediately after the ejection of theprojectile.

Referring to FIG. 1 of the drawing, a round of ammunition includes acartridge 1 and a projectile 3 in the form of a taper lock bullet. Theround is depicted in the chamber of a firearm having a barrel A, breechblock B and firing pin C, all shown schematically.

The cartridge includes a casing 5 having an external shape whichconforms to the chamber. The casing is in the form of a hollow componentthrough which extends a passage of circular cross-section having a largediameter rearward section 7, a narrowed intermediate section 9, and atapered forward section 11 which receives the trailing end of theprojectile. A frustoconical transition surface 13 extends between thepassage sections 7 and 9.

Inserted into the casing 5 from its rear end is a core 15 having ahollow rearward portion 17 and a solid forward portion 19 joined by anintermediate portion 21. The portions 17 and 19 are shaped externally soas to be a sliding fit in the passage sections 7 and 9 and theintermediate portion 21 is complementary to the transition surface 13.The portion 19 serves substantially to block the passage section 9against escape of gas therethrough.

Within the rearward body portion 17 of the core is a chamber 23 which isenlarged at is rearward end to receive an explosive primer 25. Passingthrough the intermediate body portion 21 is a plurality of obliquelyoutwardly radiating bores 27, conveniently three or four in number. Theouter ends of the bores 27 face the transition surface 13.

The chamber 23 serves as, and will be referred to herein as, the firstexpansion chamber.

When the firearm is fired, the firing pin C strikes the primer 25, whichexplodes and discharges propellant gas into the first expansion chamber23. The gas passes through the passages 27 into the space definedbetween the intermediate portion 21 and transition surface 13 of thebore. The outer surface of the intermediate portion 21 serves as apiston, so that the gas forces the core 5 towards the rear, to create asecond expansion chamber 29, as shown in FIG. 2. During this action, theforward core portion 19 is withdrawn through the passage section 7.Rearward movement of the core 15 ceases when a retaining and seal ring31 at the rear of the passage section 7 engages a stop surface 33 at theforward end of the rearward body portion 17, as shown in FIG. 3. Contactbetween the seal ring and the surface of the rearward body portion 17prevents escape of gas to the rear during the operation of the cartridgedescribed above. During this sequence of operations, upon completewithdrawal of the forward core part 19 from the forward passage section11, the gas in the second expansion chamber 29 is dumped instantaneouslyinto the passage sections 9 and 11 to expel the projectile.

The rearward movement of the core applies force to the breech block torecycle the weapon.

Because the operation of the proposed cartridge does not depend upon theuse of propellant additional to that provided by primer 25, and ejectionof the projectile takes place in response to the opening of passagesection 9 and substantially instantaneous dumping of gas into thatpassage, the proposed cartridge does not suffer from the tendencytowards unreliable operation which characterises the cartridge knownfrom EP 473 758.

Because the proposed cartridge does not have the fine passages of theknown cartridge, at least the core is especially suited to moulding fromplastics.

The cartridge may also be reused by replacing the primer or,alternatively, replacing the core and primer assembly. The proposedcartridge is also less toxic than the known cartridge because noadditional propellant is required.

The cartridge may be used as a blank if the projectile is omitted.

Although the transition surface is shown to be frustoconical, and theouter surface of the intermediate portion 21 complementary thereto, itis possible for and least the outer surface of the intermediate portion21 to extend radially, provided that bores 27 are suitably arranged tofeed gas into the second expansion chamber

What is claimed is:
 1. A cartridge for use in a firearm, said cartridgebeing capable on firing of recycling the firearm; the cartridgecomprising a casing having a projectile mounted in a front end thereofso as to extend forwardly therefrom, the casing being formed with astepped passage therethrough, the passage having a rearward largerdiameter section, a narrower intermediate section and a tapered forwardsection which receives a trailing end of the projectile; a core memberdisposed in the stepped passage, the core member having a peripheralflange at a rearward end thereof, which flange extends rearwardly of thecasing, and a forward facing piston surface and a forward portion; theforward portion of the core member being slidably received in andblocking the narrower intermediate section in an inactivated conditionof the cartridge; the core member having a defined therein a firstexpansion chamber to receive propellant gas from a primer, at least oneoutlet opening from said chamber through said forward facing pistonsurface into the passage rearwardly of a step between the rearwardlarger diameter section and the narrower intermediate section to allowgas to flow from the first expansion chamber into a second expansionchamber defined between the core member and the passage rearwardly ofthe step; such that on actuation of the primer, propellant gas isreleased into the first expansion chamber and then the second expansionchamber, wherein the second expansion chamber expands and propels thecore member rearwardly to move the forward portion to unblock thenarrower intermediate section and to allow gas to flow therethrough toeject the projectile from the tapered forward section of the passage,and wherein propulsion of the core member rearwardly serves to recyclethe firearm.
 2. A cartridge as claimed in claim 1, wherein the forwardfacing piston surface is frustoconical.
 3. A cartridge as claimed inclaim 1, wherein the forward facing piston surface extends radially. 4.A cartridge as claimed in claim 1, wherein the casing comprises aretaining and sealing ring.
 5. A cartridge as claimed in claim 1,wherein the projectile is a taper lock bullet.